1. Field of the Invention
The present invention relates to a positioner that can move an object such as a magnetic recording head, or the probe of an atomic microscope.
2. Description of Related Art
Hard disk drives contain a plurality of magnetic recording heads that write and read information from a number of adjacent rotating magnetic disks. There is typically a recording head associated with each surface of a disk. The magnetic heads write and read data by magnetizing and then sensing the magnetic field of the disks. Each recording head has an air bearing surface which cooperates with an airflow created by the rotating disk to form an air bearing. The air bearing separates the recording head from the disk surface to prevent mechanical wear. The air bearing also reduces the magnetic coupling between the head and the disk. It is desirable to minimize the height of the air bearing without inducing undesirable contact between the two components.
Each magnetic recording head is typically mounted to a gimbal of a flexure arm. Each flexure arm is attached to an actuator which has a voice coil motor. The voice coil motor can be actuated to move the heads across the surfaces of the disks to access different tracks of data. The flexure arm, gimbal and head are commonly referred to as a head-gimbal assembly (HGA). The HGA is designed to create an optimum air bearing for the recording head.
There have been developed various types of recording heads such as ferrite, thin film and magnetoresistive (MR) heads. MR heads typically have an element for magnetizing the disk (writing data) and a separate magnetoresistive element for sensing the magnetic field of the disk (reading data). As a result of manufacturing processes the MR element may be spatially offset from the write element. It is desirable to measure the offset between the two elements so that the disk drive controller can be programmed to compensate for the deviation between the read and write elements.
Recording heads are typically measured in a dynamic head tester. Dynamic head testers include a rotating magnetic disk and a fixture that can support either an HGA or an individual head. The fixture is coupled to a course positioner which moves the head adjacent to the rotating magnetic disk. The tester contains test circuitry which is coupled to the head and performs various routines to test various dynamic electrical characteristics of the head. The tester may contain a fine positioner which can move the head over very small increments to obtain test data such as the offset of an MR head. The movement by the fine positioner can be on the order of nanometers.
Some of the dynamic values measured by the tester are stored in the memory of the disk drive in which the head is assembled. It is desirable to obtain accurate dynamic values to assure a proper optimum functioning of the drive. It is therefore imperative that the fine positioner accurately move the heads during test.
Many disk drive manufacturers test every recording head before assembly into a hard disk drive. The dynamic testing therefore becomes a manufacturing step of the drive. A reduction in the time that it takes to test each recording head can save millions of dollars for the manufacturer. The test time includes a mechanical settling time for the positioner each time the head is moved relative to the disk. It would be desirable to provide a fine positioner which has a very fine resolution and relatively low settling time.
FIG. 1 shows a nanopositioner of the prior art sold by Piezosystem Jena of Germany. The Jena positioner has a piezoelectric transducer 1 that is located within an opening 2 of the positioner housing 3. One end 4 of the housing 3 is mounted to a substrate and fixed in space. A fixture (not shown) is typically mounted to the other end 5 of the housing. The application of a voltage across the transducer 1 will cause the piezoelectric material to expand and move the free end 5 of the housing along the y axis.
To provide a highly accurate positioner it is desirable to eliminate any movement of the housing free end 5 along the z axis, also referred to as out of plane movement. The Jena positioner creates an out of plane movement in the range of 80 nanometers when the free end 5 moves 100 microns. It would be desirable to provide a nanopositioner that creates less out plane movement than positioners of the prior art.